1. Field of Invention
The present invention relates to de-sizing and, more particularly, to an inexpensive and environmentally friendly method and apparatus for processing wastewater after de-sizing.
2. Related Prior Art
In dyeing, after de-sizing, there is inevitably produced a lot of wastewater including a lot of polyvinyl alcohol (“PVA”), carboxymethyl cellulose (“CMC”) and adhesive. The biodegradability of PVA, which is polymer, is poor. The pH and chemical oxygen demand (“COD”) of the wastewater are high. Hence, the wastewater is not suitable for direct release to the environment without any processing. Conventionally, an activated sludge process is executed to process the wastewater; however, the result is not satisfactory since the wastewater is rich of organic materials that cannot easily be degraded.
There have been attempts to process the wastewater by membrane separation. In the membrane separation, at least one ultra-filtration or reverse osmosis membrane is used to separate solids from liquid. With the membrane, pulp is removed from the wastewater, and the chromaticity of the wastewater is reduced, i.e., the wastewater is de-colored. Thus, met are regulations about the quality of wastewater to be released to the environment. That is, the pollution of the environment is reduced.
To avoid the reduction of the filtering rate of the membrane, an aeration apparatus may be used to produce erratic flows to remove deposit from the membrane. Moreover, a membrane bioreactor may be used to process the wastewater while reducing the deposit. The membrane bioreactor includes a turntable for supporting the membrane used in the activated sludge process. The turntable is used to produce a flow field to reduce the deposition of particles on the membranes.
The combination of the aeration apparatus with the membrane bioreactor is useful in reducing the blocking and encrustation on the membrane. The result of the processing with the membrane is however unsatisfactory for thick and viscous wastewater, and particularly so for wastewater that contains a lot of starch slurry. The starch slurry often sticks to the surface of the membrane or block pores in the membrane to form extremely viscous filter cakes. The membranes may be made of an anti-encrustation material to increase the life of the membranes. It is however difficult if not impossible to avoid rapid degradation of the flux through the membranes. It is also difficult if not impossible to wash way pulp from the surface of the membrane.
The present invention is therefore intended to obviate or at least alleviate the problems encountered in prior art.